The invention relates to a pressure medium-controlled clutch actuator, having an actuating piston, which is arranged so that it can move in an axial direction in a housing, wherein one end of the actuating piston is supported in an axial direction on an elastic diaphragm. The elastic diaphragm seals off a first area of the housing from a second area of the housing.
The invention further relates to a compressor clutch for a commercial vehicle, having a clutch actuator according to the invention.
Besides a power unit used for driving the vehicle, vehicles, particularly commercial vehicles, nowadays have a large number of auxiliary units assigned to the power unit, which are also driven by the power unit. These auxiliary units are often necessary for the operation of the vehicle, provision having to be made for operating some of the various auxiliary units continuously, and some in phases. Thus, for example, an injection pump, which delivers pressurized fuel to the power unit, must run continuously during the operation of the power unit. A pneumatic compressor, however, as may be provided in commercial vehicles for supplying pressure medium-operated service and parking brakes, may be temporarily shut down, provided that a reserve of compressed air sufficient for actuation of the brake system is available within the vehicle. The compressor may be shut down, for example, by use of a clutch, which is arranged between the power unit and the pneumatic compressor. A clutch derived from the state of the art is represented by way of example in FIG. 1.
FIG. 1 shows a clutch according to the state of the art. A compressor clutch 12 shown, which couples together friction disks (not visible) arranged in an axial direction 18 inside a housing 16, includes, in particular, a clutch actuator 10, which is responsible for the movement of the friction disks in an axial direction 18 during the operation of the compressor clutch 12. The clutch actuator 10 is pressure medium-operated, compressed air as a pressure medium, for example, being introduced into a pressure chamber having a spring 44. An actuating piston 14 is moveable in the axial direction 18 inside the housing 16, sealing webs 32, 34 sealing off the pressure chamber during the movement of the actuating piston 14. The actuating piston 14 is guided in an axial direction 18 by a bearing 42, which prevents a rotation of the actuating piston 14 during the operation of the clutch actuator 10. Also provided is a spring 44, which biases the actuating piston 14 in the axial direction 18, in order to spare the bearing 42. The spring 44 is situated in the volumes ventilated during the operation of the clutch actuator 10. The sealing rings 32, 34 may be fitted to the actuating piston 14, for example, or they may be produced directly on the actuating piston 14, a thin film of oil between the sealing webs 32, 34 and the housing 16 usually ensuring ease of movement of the actuating piston 14 with the sealing webs 32, 34 in the axial direction 18. The tightness of the ventilated volume is therefore ultimately ensured by the film of oil on the housing wall, which compensates for even the smallest irregularities. By virtue of the design, therefore, oil used as lubricant may be absorbed by the pressure medium used for operating the clutch actuator 10, and on renewed operation of the clutch actuator 10, that is to say particularly when pressure is released from the pressure chamber, can escape into the environment. This is detrimental from ecological standpoints and pollutes the environment unnecessarily, since oil expelled uncontrolledly is not readily degradable and exercises a toxic effect on many organisms.
U.S. Pat. No. 4,708,229 A discloses a known clutch actuator.
The object of the present invention, therefore, is to provide a clutch actuator for a compressor clutch, which has improved operating characteristics.
This and other objects are achieved by providing a pressure medium-controlled clutch actuator having an actuating piston which is arranged so that it can move in an axial direction in a housing. One end of the actuating piston is supported in an axial direction on an elastic diaphragm, which seals off a first area of the housing from a second area of the housing. The elastic diaphragm includes a projection on the side facing the actuating piston.
The clutch actuator according to the invention thus improves upon the state of the art in that the elastic diaphragm comprises a projection on the side facing the actuating piston. Interacting with the housing, a material reinforcement of the diaphragm in the form of a projection on the side facing the actuating piston serves to generate a force biasing the actuating piston, so that this is always situated in a defined axial position. Furthermore, the operating travel in an axial direction that has to be covered for operation of the clutch is reduced and the service life of the axial bearing of the actuating piston is increased. Since the end of the actuating piston can be supported on the diaphragm, a contact between the pressure medium and an oil used as lubricant is prevented. An uncontrolled emission of oil together with the pressure medium used is therefore reliably prevented.
The elastic diaphragm may usefully form a bellows, which is arranged at least partially inside the housing. The diaphragm itself can in this way provide a complete pressure chamber, for example in the form of a cushion or a torus, a change of pressure inside the bellows displacing the actuating piston in the axial direction through the expansion or through the collapsing of the bellows.
The elastic diaphragm may advantageously have at least one edge which is fixed in relation to the housing. Alternatively, a diaphragm, which already forms a complete bellows or which subdivides a volume inside the housing into two areas separated from one another, in order to form a bellows, may here be fixed inside the housing. Owing to the elasticity of the diaphragm, in the second case the partition wall formed is deformable and in the event of a pressure increase is capable of moving the actuating piston supported on the diaphragm in an axial direction. In the first case only the position of the bellows is defined by fixing the edge in the housing.
Here at least the one edge of the elastic diaphragm may advantageously be formed by a sealing web. Forming the edge of the diaphragm as a sealing web facilitates assembly and increases the stability of the clutch actuator.
More preferably still, the elastic diaphragm may be fabric-reinforced. This serves to increase the durability of the diaphragm and thereby of the clutch actuator as a whole.
Furthermore, the elastic diaphragm in the support area of the actuating piston may include an indentation, into which the end of the actuating piston projects. In this way the actuating piston can be supported virtually on the surface of the diaphragm, so that further guiding of the actuating piston in an axial direction may be dispensed with.
The elastic diaphragm may usefully also be of substantially circular shape. In particular, this allows force to be transmitted to the actuating piston without interference from radial components.
The actuating piston may usefully also be embodied as a hollow piston, through which a shaft of the compressor clutch is passed, and the elastic diaphragm may have an opening for the passage of the shaft. This affords an especially compact design form of the compressor clutch.
In particular here, the opening for the passage of the shaft may be of circular shape.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.